JPH08188440A - Furnace for drawing optical fiber - Google Patents

Abstract

PURPOSE: To obtain an optical fiber hardly causing the fluctuation in fiber diameter by providing a constitution for installing a shutter ring at the top of a furnace for drawing the optical fiber, providing an elastically deformable sealing ring thereon and holding the sealing ring with a sealing ring holder. CONSTITUTION: This furnace for drawing an optical fiber is constituted by placing a shutter ring 20 of a heat insulating structure for passing a supporting rod 15 therethrough in a noncontact state at the top of the furnace for drawing the optical fiber, arranging an elastically deformable sealing ring 27 so as to bring the inner peripheral surface thereof into sliding contact with the outer peripheral surface of the supporting rod 15 above the shutter ring 20, placing a sealing ring holder 30 on the shutter ring 20 so as to hold the outer peripheral side of the sealing ring 27 and pressing the sealing ring holder 30 together with the shutter ring 20 to the top side of the furnace for drawing by a ring fixing means. Thereby, an atmospheric gas in the furnace core tube is prevented from leaking out and the temperature decrease at the top of the furnace can be reduced to suppress the convection of the gas in the furnace.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber drawing furnace for drawing an optical fiber by heating and melting an optical fiber preform.

[0002]

2. Description of the Related Art When a base material for an optical fiber is heated and melted in an optical fiber drawing furnace and an optical fiber is drawn from the lower end portion of the optical fiber drawing furnace, it is necessary to prevent oxidation of a material constituting a core tube of the optical fiber drawing furnace. For the purpose, the inside of the optical fiber drawing furnace is placed in an atmosphere of an inert gas such as nitrogen or helium.

For this reason, the structure of this optical fiber drawing furnace is devised so that the above-mentioned inert gas does not flow out from the optical fiber drawing furnace, for example, Japanese Patent Laid-Open No. 6-56458 and Japanese Patent Laid-Open No. 1-56458. No. 192,740, etc. In the one disclosed in Japanese Unexamined Patent Publication No. 6-56458, a shutter that can be opened and closed is provided in an optical fiber drawing furnace, and a gap between the shutter and an optical fiber preform and a support rod that penetrates the shutter is set to be as small as possible. It is a thing. Also, Japanese Patent Laid-Open No. 1-19274
The device disclosed in Japanese Patent No. 0 is provided with a cylindrical shutter made of a heat-resistant metal that surrounds the outer peripheral surface of the optical fiber preform in a close state, and by narrowing the gap between them, the support rod and the shutter are separated from each other. The flow of atmospheric gas is suppressed from the gap.

[0004]

[Patent Document 1] Japanese Patent Application Laid-Open No. 6-56458
In the conventional optical fiber drawing furnace disclosed in the publication, the structure of the shutter is very complicated, and the sliding portion is exposed to the high temperature optical fiber drawing furnace. Various problems occur in terms of contamination in the drawing furnace and thermal durability of the shutter itself. Moreover, in order to avoid interference with the shutter, it is necessary to secure a certain gap between the shutter and the optical fiber preform and the supporting rod. The outflow cannot be stopped.

In the case of the optical fiber drawing furnace disclosed in JP-A-1-192740, the shutter is oxidized and deteriorated by the radiant heat from the optical fiber preform and the heater for heating and melting the optical fiber preform, and the optical fiber drawing is performed. It causes pollution in the furnace. Moreover, like the previous example, it is necessary to secure a certain gap between the shutter and the support rod, and it is not possible to prevent the outflow of the inert gas in the optical fiber drawing furnace from this gap. . Moreover, since the shutter is made of metal with good thermal conductivity, the upper end of the optical fiber drawing furnace facing the shutter is cooled by the outside air, and thermal convection easily occurs in the optical fiber drawing furnace. There was a problem.

In particular, in order to prevent thermal deterioration of a metal shutter, a coolant jacket is formed in this shutter to circulate a cooling liquid, and the one disclosed in JP-A-3-8738 discloses an optical fiber. As a result of this cooling liquid further cooling the upper end of the drawing furnace, a large amount of thermal convection occurs and the gas flow in the optical fiber drawing furnace is disturbed, making the diameter of the drawn optical fiber extremely unstable. Was there.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical fiber drawing furnace capable of manufacturing an optical fiber having a small wire diameter variation at a low cost.

[0008]

An optical fiber drawing furnace according to the present invention is provided with a shutter ring which is mounted on the upper end of the furnace and through which a supporting rod penetrates in a non-contact state, and which is located above the shutter ring and An elastically deformable seal ring whose peripheral surface is in sliding contact with the outer peripheral surface of the support rod, a seal ring holder which holds the outer peripheral side of the seal ring and is placed on the shutter ring, and the seal ring holder. The shutter ring is provided with a ring fixing means for pressing the shutter ring toward the upper end side of the furnace, and the shutter ring has a heat insulating structure.

Here, the shutter ring may have a lower ring that abuts on an upper end portion of the furnace and an upper ring that abuts on the seal ring holder,
It is effective to interpose a heat insulating material between the lower ring and the upper ring, and this heat insulating material is preferably an aggregate of fibers made of ceramics. A heater may be incorporated in the lower ring on the upper end side of the furnace with respect to the heat insulating material, and the lower ring is made of ceramics, particularly quartz glass, and the upper ring is made of a heat-resistant metal, especially stainless steel. Is preferably formed.
Further, it is effective to form the seal ring with a fluororubber elastic body.

[0010]

According to the present invention, the shutter ring and the seal ring are inserted from the upper end of the support rod, and in this state, the optical fiber preform is fed into the upper end of the furnace so that the shutter ring and the seal ring are superposed on the upper end of the furnace. To match. The shutter ring and the seal ring are pressed to the upper end side of the furnace by the ring fixing means, thereby closing the gap between the upper end of the furnace and the shutter ring and the gap between the shutter ring and the seal ring holder. Becomes Further, the seal ring of the seal ring holder, which is superposed on the shutter ring, is in elastically deformable sliding contact with the outer peripheral surface of the support rod, and the gap between the support rod and the seal ring is also closed.

Since the shutter ring has a heat insulating structure, the influence of radiation heat from the upper end of the furnace on the seal ring is mitigated, and conversely, the temperature decrease at the upper end of the furnace is suppressed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical fiber drawing furnace according to the present invention will be described in detail with reference to FIG. 1 showing a schematic structure thereof and FIG.

That is, in the furnace core tube 13 provided at the center of the stainless steel furnace body 12 lined with the heat insulating material 11, the upper end of the optical fiber preform 14 is supported by a support rod 15 via a chuck (not shown). It has been suspended by. In addition, an inert gas supply pipe (not shown) such as helium or nitrogen is connected to the upper part of the core tube 13 in order to prevent oxidation of the material forming the core tube 13 and the like.
An inert gas is supplied into the furnace core tube 13 from an inert gas supply source (not shown) through the inert gas supply pipe. Further, the central portion of the furnace body 12 and the core tube 1
A cylindrical carbon heater 17 for heating and melting the lower end portion of the optical fiber preform 14 to draw the optical fiber 16 is provided between the carbon heater 17 and the optical fiber preform 3. The heat insulating material 11 is arranged so as to surround the upper and lower sides and the outer peripheral side of the carbon heater 17 so that heat does not escape to the outside as much as possible.

A base material introducing cylinder 18 protruding upward from the furnace body 12 is connected to the upper end of the furnace core tube 13, and an opening through which a supporting rod 15 penetrates is formed in the upper end surface of the base material introducing cylinder 18. A shutter ring 20 having 19 formed in the center is placed. Since the opening 19 of the shutter ring 20 is set to have a diameter smaller than the outer diameter of the optical fiber preform 14, a new optical fiber preform 14 is set in the core tube 13 from the preform introduction tube 18. If the shutter ring 2
It is necessary to insert 0 into the support rod 15. The shutter ring 20 in the present embodiment is mainly composed of a lower ring 21 made of quartz glass that comes into contact with the upper end surface of the base material introducing cylinder 18 and an upper ring 22 made of heat-resistant stainless steel and superposed on the lower ring 21. The lower ring 21 and the upper ring 22 are constituted by a plurality of pairs of bolts 24 using an annular groove 23 formed in an outer peripheral portion of the lower ring 21.
These outer peripheral edge portions are tightened together and integrated by a nut 25.

Between the lower ring 21 and the upper ring 22, a heat insulating material (bulk fiber) 2 in which ceramic fibers such as aluminum oxide or silicon dioxide are gathered in a cotton shape.
6 is interposed to prevent the seal ring 27, which will be described later, from being deteriorated by the radiant heat in the base material introducing cylinder 18, and to keep the upper end portion of the base material introducing cylinder 18 warm. Care is taken to suppress the generation of thermal convection in 18. In this embodiment, the heat insulating material 26 is filled in the storage groove 28 formed in the upper end surface of the lower ring 21 in an annular shape, but it may be filled in the upper ring 22 side. In addition, an electric heater 29 connected to an external power source (not shown) is embedded in the lower ring 21 on the opposite side of the upper ring 22 with the heat insulating material 26 interposed therebetween. By energizing the electric heater 29, The lowering of the temperature of the upper end of the base material introducing cylinder 18 is prevented, and the heat insulating material 26
At the same time, consideration is given so that thermal convection does not occur in the core tube 13 and the base material introducing cylinder 18.

A pair of upper and lower annular seal ring holders 3 made of stainless steel are formed on the shutter ring 20.
0 is placed and is in a state of being pressed against the upper end surface of the base material introducing cylinder 18 via the shutter ring 20 by a ring fixing means (not shown). The seal ring 27 whose outer peripheral portion is sandwiched by these seal ring holders 30 is formed in an annular shape by a fluorine-based rubber-like elastic body excellent in heat resistance, and the inner diameter of the opening 32 at the center thereof is the same as that of the support rod 15. It is set slightly smaller than the outer diameter.

As a result, the opening 32 of the seal ring 27 is formed.
Since the support rod 15 is in close contact with the support rod 15,
The upper end opening portion of the base material introducing cylinder 18 is closed by the shutter ring 20, the seal ring holder 30, and the seal ring 27, and the outflow of the gas in the furnace can be almost certainly prevented.

Here, using the above-mentioned optical fiber drawing furnace, an optical fiber preform having an outer diameter of 50 mm is drawn into an optical fiber 16 having a diameter of 125 μm, and an electric heater 29 is energized to enclose the housing groove 28. By adjusting the amount of the heat insulating material 26 filled inside, the temperature of the portion of the lower ring 21 forming a part of the shutter ring 20 facing the base material introducing cylinder 18 side is measured with a thermocouple thermometer. Adjustment was performed stepwise in the range of 85 to 330 ° C., and the variation amount of the wire diameter of the optical fiber 16 at this time was measured. Table 1 shows the results.

[0019]

[Table 1]

As is clear from Table 1, the variation of the wire diameter becomes smaller as the temperature of the inner wall of the shutter ring 20 rises, and by keeping the temperature of the inner wall of the shutter ring 20 at 250 ° C. or higher, Wire diameter fluctuation ± 0.3 ~
It can be suppressed to 0.2 micrometer or less.

[0021]

According to the optical fiber drawing furnace of the present invention,
Since the elastically deformable seal ring whose inner peripheral surface is in sliding contact with the outer peripheral surface of the support rod is provided, it is possible to significantly reduce the leakage of the atmospheric gas in the core tube.

Since the shutter ring having a heat insulating structure is interposed between the seal ring and the upper end of the furnace, the temperature drop at the upper end of the furnace near the shutter ring is reduced, and the optical fiber drawing is performed. As a result of suppressing the convection of the gas in the furnace, the gas flow in the optical fiber drawing furnace is reduced in combination with the provision of the seal ring, and the fluctuation of the optical fiber diameter is suppressed and suppressed, and the transmission loss A small number of good quality optical fibers can be obtained. In addition, the durability of the shutter ring can be improved by forming the shutter ring with the lower ring made of ceramics and the upper ring made of heat resistant material.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic structure of an embodiment of an optical fiber drawing furnace according to the present invention.

FIG. 2 is a cross-sectional view showing an extracted and enlarged main part of the present invention in the embodiment shown in FIG.

[Explanation of symbols]

 Reference Signs List 11 heat insulating material 12 furnace body 13 core tube 14 base material for optical fiber 15 support rod 16 optical fiber 17 carbon heater 18 base material introducing cylinder 19 opening 20 shutter ring 21 lower ring 22 upper ring 23 annular groove 24 bolt 25 nut 26 heat insulating material 27 Seal Ring 28 Storage Groove 29 Electric Heater 30 Seal Ring Holder 31 Opening

Claims (9)

[Claims] 1. A shutter ring, which is mounted on the upper end of a furnace, and through which a supporting rod penetrates in a non-contact state, and an elastic member which is located above the shutter ring and whose inner peripheral surface is in sliding contact with the outer peripheral surface of the supporting rod. A deformable seal ring, a seal ring holder that is mounted on the shutter ring while holding the outer peripheral side of the seal ring, and a ring that presses the seal ring holder together with the shutter ring toward the upper end side of the furnace. An optical fiber drawing furnace, comprising: a fixing means, wherein the shutter ring has a heat insulating structure. 2. The shutter ring has a lower ring that abuts on an upper end portion of the furnace, and an upper ring that abuts on the seal ring holder.
The optical fiber drawing furnace described in 1. 3. The optical fiber drawing furnace according to claim 2, wherein a heat insulating material is interposed between the lower ring and the upper ring. 4. The optical fiber drawing furnace according to claim 3, wherein a heater is incorporated in the lower ring on the upper end side of the furnace with respect to the heat insulating material. 5. The optical fiber drawing furnace according to claim 4, wherein the temperature of the portion of the lower ring facing the upper end side of the furnace is heated to 250 ° C. or higher. 6. The heat insulating material is an assembly of fibers made of ceramics, according to claim 3 or 4.
Alternatively, the optical fiber drawing furnace according to claim 5. 7. The lower ring is made of ceramics, and the upper ring is made of refractory metal.
Alternatively, the optical fiber drawing furnace according to claim 5 or claim 6. 8. The ceramic is quartz glass,
The optical fiber drawing furnace according to claim 7, wherein the refractory metal is stainless steel. 9. The seal ring is formed of a fluorine-based rubber-like elastic body, claim 1 or claim 2, claim 3 or claim 4, or claim 5 or claim 6. Alternatively, the optical fiber drawing furnace according to claim 7 or claim 8.